I have a 32q pot and I've brewed several small 5gal runs with it (it's small). Don't forget your going to boil off some wort and there should be some room for boiling. and if your going to do BIAB you needs lots of speace for the bag. Get the biggest pot you can. Using a Keggel makes things so much easer.
I also have the SP-10 burner and 5 empty 20lb propain tanks, the 10psi reg works fine(sucks lots of LP). I do some times use my 160,000btu jet burner, but it's over kill.

Without trying to bash another product or promote ours I'd advise against that kettle. When I talked to Polarware they said the thickness of the kettle was 26 gauge which is about .5mm thick. That's the thinnest kettle I've ever seen on the market.

I picked up a 40qt aluminum pot from Cash and Carry for ~$50 out the door (no idea what the gauge is but its fairly thick). Sometimes theres just something satisfying about walking in somewhere and walking out with what you want in hand rather than waiting for it to ship to you. Would I have preferred to go stainless? Probably, but I'm kind of of the same mind set as Jake... I'm sure sooner or later I will upgrade my gear again and when I do it will likely be with the main objective of upgrading batch sizes so I figured I'd save a couple bucks by going with aluminum until I decide to throw down the cash on some keggles down the road.

As a side note... Have you considered the SQ14 over the SP10? I know the BTUs are lower of the 14 but IMHO the fact that it has a sturdy, square, four-legged base was selling point enough for me. I don't think I would trust myself around 8 gallons of boiling wort balanced on a tripod. The 14 is also plenty big enough for 5 gallons and many people have reported no problems with it for 10 gallon batches either. As a bonus the 14 is pretty impressively quite too. Just my .02

I avoided aluminum only because I've heard it's too reactive. If the consensus on this site is that aluminum is okay, I'd def. buy the next pot aluminum.

I bought a system locally that has three of the Polarware (American made) 40 qt. brew kettles and they are great. They are very well constructed, the welding and finishing on the bulkheads is top notch .

If I were starting all over again today I may look for a keg locally on CL or a scrapyard, have the top cutout a couple of bulk heads welded in or purchase weldless ones. Now you can move up to 10 gallon batches and BIAB when ready with no additional cost.

I am friends with the marketing manager of Brew Magic in Toledo. They have a really nice system and also sell individual component such a brew kettles. They are purpose-built modified kegs. They're very nice.